OSGi as a Framework for Building a Product Line:

Experience and Best Practices

Ruwan Linton (ruwan@apache.org)

&Afkham Azeez

(azeez@apache.org)

Agenda• SOA Middleware Products

• Componentized SOA Platform

• Why OSGi?

• Challenges faced

• Best practices

• WSO2 Carbon

SOA Middleware Products.Traditional SOA platforms are:• Overly complex• Heavyweight• Not internally consistent • Hard to learn• Acquired, not designed• The components don't fit well together

The result is:• centralizing SOA on a single hub based ESB• relying on the “SOA team” to solve problems• Replacing centralized monolithic applications with

- Centralized monolithic ESB and SOA platform

• Customers waste time integrating vendor's products

• Time that could be spent integrating real applicationsProduct Integration

• Adding new aspects of SOA (e.g. process choreography)

means installing and learning a completely new productContinuity

• Large SOA platform “components” are actuallydistinct products

• Bigger installations encourage centralizationSOA Deployment

• SOA adoption is restricted because tools are so difficult to use

Skills

• Heavyweight, complex and bloated

• Downloading an evaluation can take daysAgile Adoption

What is wrong with existing SOA Platforms?

Solution?• Componentized SOA Platform

– WSO2 Carbon Architecture based on OSGi

Why OSGi?• It's a framework which specifies a modular

architecture for dynamic component based systems.

• It can be used as the underlying core modularization

technology.

Why OSGi? It's a dynamic module system for Java.

– Bundle( == jar) is called the Modularization unit.

– Meta data can be specified in manifest headers.

– Separate classloader for a bundle.

– A bundle can share or hide packages.

– Allows multiple versions of the same class in a single VM. This solves jar hell problem.

OSGi services provides in-VM collaborative SOA model

– Each bundle can provide services to other bundles

– Services are simply Java objects that implement a given interface

– There is a Service Registry where you can find a service implementation

– Services should be only links between components

– Best known way to decouple components from each other.

– This allows components to be substituted.

– Significantly minimize class loading problems

Why OSGi...

Why OSGi.. • It's Dynamic

– The OSGi component model is a dynamic model

– Bundles can be installed, started, stopped, updated, and uninstalled without shutting down the whole system.

What is WSO2 Carbon?

Core Carbon Framework

Clustering

Security

T ransports Mgmt

Mgmt Stats

Logging

T ryIt

BundleMgmt

Cache

T hrot t le

KeyStoreManager

UserManager

ESB WSAS DataServices

MashupServer

ProcessServer

Registry

Proxy

MsgMediat ion

T asks

J SR181

ServiceHost ing

ServiceClients

DataSourceMgmt

DataServices

DSWizard

ScriptServices

Scraping

Gadgets

BPELRunt ime

ProcessUI

InstanceUI

Core Repos

AtomPub

SOAGovern

OSGi

What is WSO2 Carbon?• A framework based on OSGi

– Uses Equinox by default

• Still very closely based on Apache technology– Apache Axis2, Apache Synapse, Apache ODE

– Apache Tomcat, Apache Axiom, and many other core libraries

• A well defined component model for Enterprise Middleware

Core Carbon Framework

Security

Mgmt

AdminUI

BundleMgmt

Clustering Transports

Stats

Enterprise Service Bus

Security

Mgmt

AdminUI

BundleMgmt

Clustering Transports

Stats

Tasks

Proxy

MessageMediation

CoreRepository

Web Services Application Server

Security

Mgmt

AdminUI

BundleMgmt

Clustering Transports

Stats

JSR181

ServiceClients

ServiceHosting

DataServices

DataSourceMgmt

DSWizard

CoreReposity

The Full Component Repository

Security

Mgmt

AdminUI

BundleMgmt

Clustering Transports

Stats AtomPub

JSR181

ServiceClients

ServiceHosting

Tasks

Proxy

MessageMediation

ScriptServices

Gadgets

Scraping

InstanceUI

BPELRuntime

ProcessUI

DataServices

DataSourceMgmt

DSWizard

Core Repos

SOAGovern

A distributed example

Registry

DB2 Mainframe

Data Services and XSLT

ESB clusterRouting and

Logging

Mashup Server Gadget-based

UI

Server

POJO Servicesand Business

Process

Unified Console

Unified management console

Can be run independently and connect to any JVM instance

Use case: Data services & mediation

• Daniel is a Database Administrator– He has used WSO2 Data Services to expose his Data as

Secure Web Services across the Enterprise

– Now he has been asked to implement an existing schema

– By adding the Mediation component and using XSLT or E4X he can effectively convert the existing service interface to match the corporate schema

Security

Mgmt

AdminUI

BundleMgmt

Clustering Transports

Stats

Transform

DataServices

DataSourceMgmt

DSWizard

Core Repository

Use case: POJO service and logging

• Helen is a POJO Service developer– She has an existing POJO service

– The analytics department would like her to send a copy of every service request to them

– She could write a new Handler in Java, but she discovers it takes 5 minutes to deploy and test the ESB Clone Mediator

Security

Mgmt

AdminUI

BundleMgmt

Clustering Transports

Stats

JSR181

ServiceClients

ServiceHosting

Message CoreRepostyMediation

Challenges

• Difficult to convert existing code into OSGi bundles.

• Legacy jars use class loaders heavily, hence most likely to fail in an OSGi environment.

• Getting the “start level” of bundles right is hard.

• No built in support for JSPs in the model

• Originally designed for embedded devices

• Needs little more tuning to fit into the server runtime.

• No support for the new servlet-api specs even in the latest OSGi R4 spec

Getting Started1. How to convert an existing project into OSGi• First create a big OSGi bundle including all your project code and

dependent jars.

• Use a BundleActivator to call the main class.

• Get your project working.

• gradually break down the big bundle into manageable bundles.

– remove all the dependent jars and use their OSGified versions.

– If possible, break down your project into reusable components(bundles)

• You will get so many issues.

• Solve them and keep it working!!

• Use Ant/Maven bundle plugin to create bundles.

Best practices..2. Use proper package imports.• Import all the packages your bundle needs

• Use version when importing packages

– This avoids version conflicts.

– Fixed versions vs. version ranges.

• User Import-Package instead of Require-Bundle

– Import-Package can have many providers

– Require-Bundle can only have a single provider.

• Avoid using Class.forName

– a lots of ClassNotFoundExceptions.

– Use OSGi services to handle these dynamic collaborations between bundles.

– As a workaround for Class.forName, use DynamicImport-Package. But this is not the

recommended approach.

Best practices..

3. Avoid start ordering dependencies.• Starting order of bundle may differ on different framework.

• Use ServiceTracker utility or Declarative Services

4. Whiteboard pattern.

• The whole platform was designed to be consistent

• The products integrate using the Registry out-of-the-boxProduct Integration

• Can install new function into an existing deployment

• The same Admin UI works for all productsContinuity

• Choose the components you need

• Total platform is <150Mb (1/4 the size of Oracle)

• Designed for Distributed Deployment with a central registrySOA Deployment

• Based on industry standards

• Common patterns can be applied across productsSkills

• Start with the components you need, and grow as neededAgile Adoption

What is right with Carbon?

Powered by OSGi OSGi is the underlying core modularization technology

– Shipping with Eclipse Equinox by default

– Can be supported on Spring dm Server, Felix and Knoplerfish if required

• Uses the core OSGi approach to support plugging in new function in a managed way

• Any OSGi bundle can be deployed (e.g. ActiveMQ)

• New components can be deployed into an existing installation

• Used for both server runtime as well as for componentized management console

• Customers can write and deploy their own OSGi components

But more than just OSGi• Analogies:

– Eclipse uses OSGi but is much more – it defines how you plug Tool components into a Tooling Framework

– Microsoft Office uses DLLs, but is much more – it defines how you can share a graph component across multiple document types

• Carbon uses OSGI, but it also defines how you build a consistent SOA platform

– New service types plug into the console

– Security, throttling, stats, TryIt, all work on any service component

• Not just using OSGi for componentizing a single product, but rather entire middleware platform

Summary

Highly adaptable to real SOA deployments– Adapt your middleware to your enterprise

architecture, not your architecture to the middleware